How to Close Tab/Window
Edit : Make sure you are using a mouse with right-click capability.

Right click on the tab and choose Delete



If the popup doesn't appear then there is something wrong with your installation or this is a bug. 

You might try resetting Blender to factory settings or there is a hidden feature I do not know in the preferences to disable it...

To reset to factory settings (Caution this will revert every setting you changed after the installation)